As a continuation from my last point:
Most everyone would say that Blockland is for kids because it is LEGOs on the computer. Most kids don't give a crap about amazing graphics, especially when a lot of kids don't even have a computer that could run that sort of thing and would end up disabling it anyway. Then they would look at videos and pictures from past version of Blockland and wonder, "Why can't we have that?" After a while, either soon or not so soon, people will eventually be asking for maps with terrain again because they forgot how much fun it was exploring new maps or playing hide and seek or something on a map with interiors, or would want to experience that for themselves.
Blockland is about building what you want, where you want it whatever it might be. Sacrificing the two features that define maps from each other for one feature that we don't even need is just pointless and stupid. It might seem nice at first because it's newer, but is it really more fun?